Wind energy is a key to the nation's 2030 goals of increased energy independence and reduced environmental impact stemming from power generation (Lindenberg et al. 2008). It is projected to account for as much as 20% of U.S. power by 2030. This sustainable source will improve the nation's energy independence and allow a low environmental impact as compared to traditional fossil fuels in many ways. Firstly, it can reduce energy related emissions since the 20% wind penetration by 2030 is estimated by the U.S. Department of Energy (DOE) to avoid 2,100 million metric tons of carbon into the atmosphere. Secondly, estimates by Jacobsen (2009) indicate that 300 GW of wind power primarily used for charging electric-battery vehicles would eliminate 15,000 emissions-related deaths per year by 2020. This would also eliminate 15 million barrels per day of imported oil in the United States, reducing the amount of imported energy and increasing our energy independence and security.
Maintaining or lowering cost of energy while simultaneously ramping up total installed penetration may benefit from revolutionary advances in turbine concepts at extreme-scales (diameters of 120 meters and beyond) with improved efficiency. This increase in scale and efficiency has been evident in recent wind turbine design. The average wind turbine rated power has increased twenty-fold since 1985, with present systems averaging 2 MW. Economies of scale and higher winds aloft are driving systems to power levels of 5 MW and beyond with rotor diameters (D) nearing 120 m and greater. While larger systems are needed in the future, blade weight (currently proportional to D2.35) has become a constraining design factor due to high gravity loads (Ashwill, 2009). This scaling is important since system costs generally scale linearly with system weight and the rotor itself accounts for about 23% of the initial total system cost (Fingersh, 2006). In addition, noise (and visual) production is likely to be very significant for extreme-scale systems indicating that such systems are best suited for off-shore siting. Such siting may also reduce many existing environmental impacts but leads to complications in terms of installation and maintenance. These problems are compounded by upwind turbine configurations since such designs necessitate stiff blades to avoid rotor-blade tower strikes. Moreover, overly rigid rotor/tower systems lead to problematic high frequency fatigue loads.